As known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in containers made of sterilized sheet packaging material.
A typical example of this type of containers is the parallelepiped-shaped container for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may include a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat-sealable plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic containers for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-sealable plastic material, and is in turn covered with another layer of heat-sealable plastic material forming the inner face of the container eventually contacting the food product.
Containers of this sort are normally produced on fully automatic packaging machines, which are fed with a web of packaging material that is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating. The web of packaging material so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with a sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, containers.
Alternatively, the packaging material may be cut into blanks, which are formed into containers on forming spindles, and the containers are filled with the food product and sealed. One example of this type of container is the so-called “gable-top” container known by the trade name Tetra Rex (registered trademark).
To open the containers described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a pouring spout, defining a through pouring opening and fitted to a hole in a wall of the container.
When producing the opening device, the opening of the pouring spout is sealed by a closing element connected integrally to the pouring spout and detachable from it along a normally circular tear line. The closing element extends at the same level as the packaging material, so as to seal the hole in the wall of the container. On the side facing the lid, the closing element has an integral projecting pull ring, the free end of which is pulled by the user to detach the closing element from the pouring spout along the tear line and so open the pouring opening. More specifically, the pull ring extends inside, and at a predetermined distance from, the pouring spout.
It is also possible to fix the closing element of the opening device directly over a prelaminated hole in the packaging material, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material.
In both cases, a removable, e.g. screw or hinged, lid, is subsequently fitted to the pouring spout in order to outwardly close the latter.
According to another solution, the closing element of the opening device is formed in one piece with a protruding portion extending inside the pouring spout and welded to the lid. The latter is provided with a disk-shaped welding promoting element that is welded to the protruding portion so that, when removing the lid from the pouring spout, the protruding portion and the closing element remain attached to the lid.
In any case, the containers are formed, filled and sealed in a filling machine. When coming out from the filling machine, each container has a neck that defines the pouring spout. The neck is closed by a respective closing element, and protrudes from a top wall of the container.
Downstream of the filling machine, there is provided an applying unit for applying lids to the necks of the containers.
The applying unit comprises a conveyor along which the containers are advanced, a distribution unit that releases a lid to a respective neck, while the container is being advanced by the conveyor, and a capping unit that screws the lid onto the neck. The capping unit comprises a pair of belts. Each belt has an active branch that is substantially parallel to the active branch of the other belt. The active branches move along opposite directions and interact with diametrically opposite portions of the lid, so as to rotate the lid and screw the lid onto the neck.
A drawback of the known applying units is that they are not very precise. The belts, in fact, may become worn, thereby affecting the positioning of the lids and the screwing torque.
The known applying units apply the lids owing to the friction between the belts and the lids. The performances of the known applying units, therefore, depend on the settings and on the adjustments and fine tuning carried out by the operator. The known applying units, therefore, may be scarcely reliable, especially when the production rate is high.
In addition, the known applying units are not very flexible. In other words, major re-arrangements are required in case the size and shape of the containers on which the lids have to be applied are changed.
Moreover, since the belts interact with diametrically opposite portions of the lid, the known applying units are only suitable for applying round, or substantially round, lids.